This invention relates to semiconductor devices and, more particularly, to Schottky barrier devices.
Schottky barrier devices are widely used in many consumer, commercial and other applications. A Schottky barrier is a potential barrier formed at a metal-semiconductor junction, which has rectifying characteristics. Many Schottky barrier devices use wide bandgap semiconductors, such as silicon carbide, gallium nitride and/or gallium arsenide, which may be used for high power, high temperature and/or microwave applications. Semiconductor Schottky barrier devices include Schottky diodes, High Electron Mobility Transistors (HEMTs) and MEtal Semiconductor Field Effect Transistors (MESFETs). A HEMT is a field effect transistor that incorporates a junction between two materials with different bandgaps (i.e., a heterojunction) as the channel, instead of a doped region, as is generally the case in integrated circuit field effect transistors. A Schottky barrier gate is used to control a two-dimensional electron gas (2DEG) between a source region and a drain region. In a MESFET, a Schottky barrier gate is used to control conduction in a channel that is formed between source and drain regions.
A wide bandgap Schottky barrier device generally includes a wide bandgap semiconductor layer and a Schottky barrier metal layer on the wide bandgap semiconductor layer that forms a Schottky junction therewith. A current spreading layer is also provided on the Schottky barrier metal layer remote from the wide bandgap semiconductor layer. In order to reduce or prevent undesired mixing between the Schottky barrier metal layer and the current spreading layer, a diffusion barrier is often provided between the Schottky barrier metal layer and the current spreading layer. Thus, for example, in a gallium nitride-based device, the Schottky barrier metal layer may comprise nickel, the current spreading layer may comprise gold, and the diffusion barrier may comprise platinum.